Constriction of blood flow could improve athletic performance

Forget illicit drugs and questionable supplements. New research suggests that a small, constrictive band that wraps around an athlete's arms or legs may lead the next wave of performance-enhancing fads in competitive sports.

So, in just a few minutes' time and with minimal effort, athletes were able to significantly boost their performance, making gains that -- according to the authors -- would normally take an average of two years of intense training to accomplish.

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The study builds off research first conducted in the 1980s by cardiovascular pioneer Keith Reimer that examined infarcts, areas of dead cardiac tissue that resulted after heart attacks, when blood flow (and, hence, oxygen) were cut off for extended periods of time. Reimer and his colleagues discovered that much less heart muscle deteriorated when the tissue had previously experienced a few training sessions where blood flow was slightly reduced.

It was as if practice makes perfect, and the previous bouts of low blood flow, which researchers refer to as ischemic preconditioning, primed the heart muscle to endure more serious, even catastrophic, events. When a life-threatening heart attack transpired, instead of shrivelling away, the preconditioned heart muscle seemed to stand strong.

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In 2009, a research team led by Maria Hopman from Radbound University in the Netherlands posed a question: If Reimer's team was able to use ischemic preconditioning to protect the cardiac muscle during a heart attack, would the technique protect different types of muscle tissue from the stress and damage that occurs during another type of ischemic event, like exercise?

Though immensely different than a heart attack, exercise is technically an ischemic event, as athletic performance hinges on how much blood reaches a tissue. And insufficient blood flow, which also translates to reduced oxygen and nutrient delivery, can be one factor that limits exercise duration and intensity.

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Hopman recruited 15 healthy, trained cyclists, asking each participant to complete two maximum effort bicycling tests, where the intensity was slowly ramped up over time. But before one of the bicycling tests, the subjects underwent three 5-minute rounds where an inflatable cuff, similar to what's used to measure blood pressure, limited the circulation to their legs, followed by a five-minute rest period where the cuff was deflated.

The researchers found that the subjects performed better when they underwent ischemic preconditioning before the exercise trial, touting gains in both maximum power (1.6 percent) and peak oxygen consumption (3 percent).

Yet, the performance improvements were not due to differences in heart rate, respiration or lactate levels, all of which seemed to stay the same, regardless if ischemic preconditioning was used or not. Rather, it seemed possible that the ischemic preconditioning treatment may have given the participants their edge.

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While Hopman's work recorded the benefits conferred to the average athlete, the latest research from Wells and Redington pushes the understanding of ischemic preconditioning one step further, looking at whether the technique works in elite athletes, a group whose bodies run with machine-like efficiency.

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Using a group of 16 to 18 swimmers who previously competed at the national or international level, the research team devised a double-blind crossover study where the same athletes swam mid-intensity and maximum-effort trials, but on two different days.

To counterbalance one of the main criticisms of the earlier studies conducted by Hopman -- that the study design potentially allowed the placebo effect to creep in, inadvertently making participants try harder when they had an inflatable cuff strapped to their legs preceding exercise -- Wells and Redington decided to alter their protocol: On both days of the experiment, a cuff would be inflated on every athlete's arm. On one day, to induce ischemic preconditioning, the cuff would be pumped up enough to surpass the systolic blood pressure, slowing the flow of blood to the arms for four cycles of five minutes. The other day, the cuff was still inflated, but only enough to slightly squeeze the muscles for each 5-minute period, which provided a better sham, or control condition, than Hopman used.

Yet it seems that ischemic preconditioning is not a placebo effect at all. Similar to the Hopman's findings in average, healthy volunteers, Wells and Redington found that when elite athletes used ischemic preconditioning before the maximum-effort trials, they swam faster. In fact, the athletes bettered their personal records by 1.1 percent on average.

And just as Hopman observed, the performance boost was not a result of heart rate or blood lactate-level differences.

Consequently, ischemic preconditioning had no effect on the less rigorous, mid-intensity trials.

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All of the researchers investigating ischemic preconditioning seem to agree that temporarily reducing the blood flow to a tissue causes protective molecules to be released into the bloodstream. But many are still scratching their heads as to why.

Hopman thinks ischemic preconditioning may cause vessels to dilate once blood starts flowing again, increasing nutrient and oxygen delivery to the formerly deprived tissue. Wells and Redington, on the other hand, think altered metabolism of mitochondria -- the energy powerhouses of muscle cells -- may contribute to more energy available for exercise.